Genetic algorithm optimization of two natural gas liquefaction methods based on energy, exergy, and economy analyses: the case study of Shahid Rajaee power plant peak-shaving system

Power plants have problems supplying fuel in the cold season due to the high domestic demand for natural gas. Therefore, they use alternative fuels such as diesel and fuel oil, which reduce the plant's efficiency and cause environmental problems. Fuel peak-shaving is a solution that means liquefaction and storage of natural gas in hot seasons and then using it in cold seasons. Two cycles of the PRICO and LIMUM3 liquefaction methods, which are the two most peak-shaving cycles in natural gas liquefaction, have been studied and optimized for the case study Shahid Rajaee power plant in Qazvin city, Iran. By performing energy, exergy, and economy analyses, these two cycles are compared. A genetic algorithm is used to optimize and find the appropriate values of the key parameters. Using optimization, the SEC value in PRICO and LIMUM3 cycles experienced +0.15 and +0.12 improvement, respectively. PRICO with SEC value of 0.268 performed better than the other cycle with a value of 0.317. The annual capital expenditure (CAPEX) of the PRICO cycle was 9.12 million $, which is higher than the other cycle by 7.58 million $. The annual cost of operation (OPEX) is saved in the PRICO cycle due to the lower SEC and power consumption. The annual total cost of PRICO is 23.81 million $, which is 6.1% less than that of the LIMUM3 cycle. Finally, by comparing the results, the PRICO cycle was found to be more suitable than LIMUM3 for the peak-shaving of the Shahid Rajaee power plant.